Tech stocks have soared over the past year, pushing the Nasdaq composite index up 30 percent over the past 12 months, more than twice as much as the Dow Jones industrial average. Netflix and Facebook have doubled in price in that time.

“The big highfliers have done really well, and so I think there's been some profit-taking,” said Randy Warren, chief investment officer of Warren Financial Service.

The Nasdaq lost 50.4 points, or 1.2 percent, to close at 4,226.39.

Other indexes also fell, but not as much. The Standard & Poor's 500 index fell 9.08 points, or 0.5 percent, to 1,857.44. The Dow Jones industrial average fell 26.08 points, or 0.2 percent, to 16,276.69.

Stocks drifted lower early Monday as traders feared that sanctions against Russia could tip the world's ninth-largest economy into recession. Investors were also reacting to news that Russian troops had seized Ukrainian ships and military installations in the Crimean peninsula. Russia annexed the region last week.

Biotechnology stocks, another sector that has soared over the past year, extended a decline that began Friday after U.S. lawmakers questioned the pricing of a Hepatitis C drug made by Gilead Sciences.

A popular fund tracking biotech stocks, the iShares Nasdaq Biotech ETF, fell 3 percent on Monday. It's been up 53 percent over the past 12 months.

“It's the richest part of the market, so ... you're going to get nervousness,” said Jerry Webman, chief economist of Oppenheimer Funds.

Among stocks making big moves:

_ Herbalife rose $3.32, or 6.7 percent, to $52.86 after agreeing to back billionaire Carl Icahn's three nominees for its board. Icahn is a supporter of the embattled health supplements company in its fight with another famed investor, William Ackman, who has accused the company of operating a pyramid scheme.

_ Apple bucked the downward trend in technology stocks. The company rose after The Wall Street Journal reported that Apple is in talks with the giant cable provider Comcast to offer a streaming video service. Apple rose $6.32, or 1 percent, to $539.19.